Thank you for bringing this to our notice. I see the problem. We will take this up immediately. While I am not sure if we will fix it for the already released versions, we will definitely fix this for the upcoming ones.

There are two workarounds for this:
1. You can drag the keyframes themselves rather than the band between them.
OR
2. You could go to the Keyframes view and do the editing there. To get to this view, click on the clip, take the Current Time indicator line (CTI) on it, and go to Applied Effects button on the right side of the app towards the top. This will expand a view and has a button which expands the keyframes view. The button is a clock shaped icon to the right of the text "Applied Effects". This view should also allow you to edit it more closely.